In system virtualization, multiple virtual computing systems are created within a single physical computing system. The physical system can be a stand-alone computer, or alternatively, a computing system utilizing clustered computers and components. Virtual systems are independent operating environments that use virtual resources made up of logical divisions of physical resources such as processors, memory, and input/output (I/O) adapters. System virtualization is implemented through some managing functionality, typically a hypervisor technology. Hypervisors, also called, virtual machine managers (VMMs), use a thin layer of code in software or firmware to achieve fine-grained, dynamic resource sharing, within virtual computing systems. For example, hypervisors are the primary technology for system virtualization, because they provide the greatest level of flexibility in how virtual resources are defined and managed.